fix DelayUs using millisecond variants by typo

Improve DelayMs/DelayUs implementations

Use enum variants in the SPI driver

use --target for CI checks

use GHA

implement DelayUs for Delay

update nb dependency

Use the correct RTC counter register

fix overlapping clock ranges

fixed `PeripheralAccess::value()`

The lack of `& 1` caused using pins other than the highest numbered one
as an input to not work correctly due to misinterpreting garbage bits as
setting the pin in the high state. `&`ing with `1` solves this problem
by zeroing out bits that should be ignored.